Machines, including vocational vehicles, off-highway haul trucks, motor graders, wheel loaders, and other types of large machines associated with construction, mining, and other industries often include implements (e.g., bucket loaders) and steering components powered via hydraulic pressure. To provide hydraulic pressure for operation of such implements and components, one or more hydraulic pumps have typically been included on such machines.
Hydraulic pumps associated with a machine may be driven by a power source associated with the machine and the resulting pressurized fluid may operate the desired components of the machine (e.g., steering and implements). This operation of hydraulic pumps may exert a torque on the power source based on pump discharge pressure (e.g., a function of overall load on the pump) and a flow rate associated with the hydraulic pump, among other things. This torque may, therefore, draw a countering torque from the power source such that the power source may continue to operate with less available torque for countering other loads (e.g., accelerating the machine). The torque available from the power source may depend on numerous factors such as, for example, power source size and power source speed, among other things.
Because power sources are typically torque limited, it may be possible to apply a torque load greater than what an associated power source can provide. Therefore, a simultaneous loading from hydraulic pumps and machine acceleration may prevent an associated power source from increasing its speed, which may cause an apparent lack of response and/or power from the machine, among other problems. Where the torque associated with the hydraulic pump approaches or exceeds the operational limitations of the power source, the power source may lug or even stall.
Additionally, government standards associated with power source emissions have increased the burden on manufacturers to reduce the amount of particulate matter and other emissions that may be exhausted from power sources associated with their machines. Because steering and implement loading may affect such emissions (e.g., via torque loading), it may be desired to exert additional control over the torque load placed on a power source.
Variable displacement hydraulic pumps may allow for some control of the torque associated with a hydraulic pump by introducing a flow control mechanism (e.g., a swash plate) into the hydraulic pump. Using load sense pressure feedback signals, flow from the pump may be modified based on numerous factors including steering and implement load.
One system for controlling a variable displacement hydraulic pump is disclosed in U.S. Patent Application 2005/0071064 to Nakamura et al. (“the '064 publication”). The '064 publication includes a signal processing system designed to receive environment variables associated with operation of a power source and a variable displacement hydraulic pump. The signal processing system may then modify a pilot pressure fed back to the variable displacement pump based on the environment variables, to effect a reduction of flow and, therefore, torque associated with the variable displacement hydraulic pump.
While the '064 publication may control torque reduction associated with a variable displacement hydraulic pump, the '064 publication is directed to a machine with a targeted optimal speed of an associated power source (e.g., 2500 revolutions per minute (RPM)). Therefore, the system and related environment variables of the '064 publication may not be suitable for use in application where a power source speed is transient. Further, the '064 publication considers latent parameters associated with a driving power source (e.g., engine speed), thereby utilizing reactive measures to control power distribution, which may ultimately affect control precision. Moreover, the '064 publication fails to consider resulting emissions (e.g., smoke) when determining how the torque should be modified. Because emissions standards have become more stringent, additional limitations may be considered during operation of a hydraulic pump at a particular flow rate and pressure, such that emissions meet government requirements.
The present disclosure is directed at overcoming one or more of the problems or disadvantages in the prior art control systems.